The present invention relates to a system for optimally starting and stopping air treatment within a building so that the building can be controlled during non-occupancy times at a level requiring minimum energy consumption and, more particularly, to a system which is adaptive so that the optimum stop and/or start times are adjusted based upon the accuracy of prior start/stop times.
Present building control systems, whether for very large buildings or for very small buildings, are primarily concerned with conserving energy. It is the primary objective of these systems to reduce the energy consumption of a building to the lowest possible level. One of the most important energy conserving practices today is the setback of the indoor temperature of a building during non-occupancy hours. During the winter months, this setback practice involves lowering the setpoint of the indoor temperature so that the heating system will not run as much during periods of non-occupancy and, therefore, requires less energy consumption. During summer months, setback means raising the indoor setpoint temperature so that the air conditioning system is not required to run as much during non-occupancy hours and, therefore, requires less energy consumption than is required during occupancy hours.
In order for the building to be comfortable by the beginning of an occupancy period, previous systems have determined at what time the air treatment system, whether it is an air heating furnace or an air conditioning chiller system, must be turned on prior to the beginning of occupancy in order to bring the indoor temperature to the desired occupied setpoint temperature. Typically, the amount of time that the air treatment system is energized prior to the beginning of occupancy has been determined by the outdoor air temperature. During the winter, if the outdoor air temperature is cold, then the amount of time required to bring the indoor temperature to the desired setpoint is long, and if the outdoor temperature is warmer, the amount of time is shorter.
Conversely, energy can be saved by stopping the air treatment equipment for a time prior to the period of non-occupancy so that the inside space temperature drifts to the minimum established comfort level at the time non-occupancy begins and thereafter controlling the air treatment equipment at the night setback temperature. This operation is termed optimum stop. Again, the amount of time prior to the period of non-occupancy that the air treatment equipment can be deenergized is a function historically of outdoor temperature.
Although most of these prior art systems wherein the amount of start up time before occupancy and stop time before non-occupancy required to maintain a comfort level during occupancy and a setback level during non-occupancy have been based upon outdoor temperature, there have been attempts to use space temperature as the basis for determining these start and stop times. In such a system, the rate of change of the temperature during periods of occupancy and non-occupancy have been used in order to determine optimum start and stop times. However, such systems are not adaptive. There are many factors other than outdoor temperature and/or rate of temperature change within the building which may impact optimum start and stop times.